The 1 mile communication radius covers basically the whole city (at least if the map so far
has an accurate scale, and it probably has a fairly fuzzy border where communication slowly fades, rather than a precise cutoff.
So we probably can't use the border to pinpoint each other, but we do have a sense of where the other is (places my crystal has been count as places I have been for the purposes of teleportation).
PS - Nobody has mentioned the auras on the Archa yet.
especially Abjuration, Conjuration, and Enchantment
I can see strong Abjuration and Conjuration spells as part of a defensive array... but Enchantment?
- Some sort of odd buff, like amped Aid, or "symbol of inspire loyalty"
- A shapeshifting stand-in, enchanted for further compliance
- The archa is a mind-controlled figurehead (who knows for how long)